Very nicely written and well done. HOWEVER -

A J-head weighs about 200 pounds. Mine was sitting on a rolling dolly, oriented
90° from the way it normally sits on the mill. The bolting surface was oriented
so that it was down towards the floor, and it was actually sitting on a wooden
box. The belt guard hung down behind the box, and rested on a V-block. When I
lifted up the front of the mill head, that meant the back, now supported at just
one point, was VERY TIPPY. The combination of very tippy and very heavy made me
very nervous. This is the key to my entire dilemma. I could just barely lift up
the mill head and slide the plate under it, then punch it and get it out,
without something horrible happening, and I felt I'd done yeoman duty when it
was all done safely. I would have happily followed your procedure, or done
something very similar, but for the extremely constrained circumstances.

It might have been easier later on, once I got it up in the air with the engine
hoist, but then there would have been nothing to punch *against*.

I thought about just punching the holes I did mark using the transfer punch, and
then using that piece as a template to mark another piece, but here my Scottish
heritage came into play. Steel isn't free, far from it, and why waste one piece?

Much more satisfying and better to just drill the correct bolt pattern.

GWE

DeepDiver wrote:

I'll offer the following alternative solution in the event that actual
published specs aren't available for a future project with similar
difficulties:

1. Get a sheet of material to use as a pattern transfer that's larger than
the mating face of the item in question. The sheet can be a paper product
(like tag board or index card stock) or it can be sheet metal (aluminum or
steel) for more demanding tolerances.

2. Place the sheet under your item so that the sheet extends beyond the
mating flange in all directions.

3. Using either a fine pencil (I like 0.5mm mechanical pencils) on paper, or
a sharp scribe on sheet metal, trace the outline of the mating flange onto
the sheet. If necessary to help see the scribed lines, you can apply some
layout blue first.

4. Now you can use your transfer punches to transfer your hole positions. I
doubt if 1/64" play would matter in an application like this one. (Since
you're using bolts to affix the head to your adapter plate, you need a
certain degree of clearance anyway in your holes. If you're transferring
holes for locating dowel pins, that's another story.) Anyway, if the
wobbliness of the transfer punch concerns you, and you don't have an
intermediate size that will fit snuggly, here's a trick I've used that works
well (although, again, I wouldn't recommend it for high-precision work):
take the largest transfer punch that will fit the hole and wrap it tightly
with adhesive tape to help center it in the hole. You don't want to use a
soft or spongy tape (e.g., duct tape or electrical tape); I've used thin,
clear plastic packing tape with success. It shouldn't take more than a
couple of layers of tape to fill the gap; if it does, your transfer punch is
too undersized.

5. Now that you've transferred your pattern to the sheet, you can use the
sheet to transfer the pattern to your workpiece. You can cut out the pattern
if you wish along the line made around the flange, or you can make centering
marks to align your workpiece on the sheet, or any number of alternatives.
You can work from the front, or from the back (taking into account that the
pattern will be mirror-reversed on the opposite side) as long as the marks
are visible on the back side. (You may want to punch or drill small holes
through sheet metal where the transfer punch marks are.)

Hope this helps.

- Michael